Carbon Dioxide

CARBON DIOXIDE (carbonic anhydride, carbon dioxide, CO₂) was known as early as the 16th century to Paracelsus and van Helmont as a component of air and as a product formed during fermentation, respiration, etc. Carbon dioxide is colorless, has a weak odor and slightly acidic taste. Its density is almost 22 times greater than that of hydrogen and 1¹/₂ times greater than that of air. CO₂ is known in three states. Carbon dioxide passes into the liquid state at 0° under a pressure of about 36 atm.; critical temperature +31.4°; liquid carbon dioxide is colorless, does not mix with water, dissolves in alcohol, ether, and oils; at 0° its specific gravity is .9. When flowing out into the air from a vessel under pressure, carbon dioxide turns into a solid snow-like mass, which, evaporating rapidly, bypassing the liquid state, lowers the temperature to -78°; water, mercury, and other substances freeze from contact with this mass. In the solid state, especially after being compressed into a dense mass ('dry ice'), carbon dioxide is preserved quite long in the air, since it requires even more heat to turn into gas than liquid CO₂. Dry ice has wide application in technology, laboratories, and transportation for obtaining low temperatures. Carbon dioxide dissolves well in water, alcohol, and other liquids. At 0° one volume of alcohol dissolves 4.3 volumes of CO₂, water at 0° and 760 mm pressure dissolves 1.5 volumes, at 10-12°-1 volume. The hydrate (H₂CO₃) formed upon dissolution in water, carbonic acid (carbon dioxide), is not known in the free state, since as it forms it decomposes into CO₂ and H₂O. Carbon dioxide has weak acidic properties (pH=approx. 6.1); its solutions turn blue litmus red, which disappears upon standing; as a dibasic acid it gives normal and acid salts, carbonates and bicarbonates; salts with alkali metals - both acid and normal - dissolve well in water; alkaline earth salts acid ones dissolve, normal salts do not dissolve. Carbon dioxide does not burn and does not support combustion; only a few substances are capable of taking oxygen from it, e.g. Mg, K burn in carbon dioxide, with carbon being released. Carbon dioxide is very widespread in nature, found in the free state and in various compounds; in the free state it is found in the air, in water; in the form of compounds (MgCO₃, FeCO₃, limestone) it is part of the earth's crust. The presence of CO₂ in water gives it the ability to dissolve various salts (phosphoric, calcium carbonate), as a result of which the destruction of rocks occurs. Carbon dioxide is released by volcanoes, from mountain cracks, in some caves, springs, etc. Carbon dioxide is formed during respiration of animals and plants, during decay and fermentation, during combustion of organic substances. The green parts of plants in the light absorb CO₂ and form carbohydrates from it (see Assimilation, Carbohydrates). In the animal body carbon dioxide is present as a product of oxidation of organic substances, in tissues and fluids - both in the free state and in combination, in the form of carbonates. Carbon dioxide is a respiratory hormone that acts as an irritant to the respiratory center (see Respiration, Blood Gases). The release of carbon dioxide from the blood in the lungs requires its preliminary transformation of H₂CO₃ into anhydride, CO₂. Meldrum and Roughton believe that this process (as well as the hydration of CO₂ into H₂CO₃) is catalyzed by a special enzyme (carbonic anhydrase). Carbonic acid and its salts are one of the main buffers of the blood, maintaining the constancy of its active reaction (see). The amount of carbon dioxide released is judged by the intensity of metabolic processes in the body. To determine the carbon dioxide released during respiration, methods of Pettenkofer, Peterson-Palmquist, and others are used. Pettenkofer's method is based on the absorption of carbon dioxide by a solution of barium hydroxide and determining the excess of the latter by titration. A simpler and faster method is that of Peterson-Palmquist. Carbon dioxide and its compounds have wide practical application. Carbonated waters are used for medicinal purposes in the form of baths and internally. It is believed that carbon dioxide acts as a stimulant on gastric secretion. Carbonated water quenches thirst well, which is why it is recommended to drink it during work at high temperatures. Carbon dioxide is used in chemical productions in the preparation of soda, white lead, etc. Carbon dioxide is obtained in factories either by burning coal or by the action of acids on lime; it can also be obtained by calcining dolomite (MgCO₃) and other compounds. In laboratories, to obtain carbon dioxide, Kipp's apparatus is used, acting on marble with hydrochloric acid.

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Carbon dioxide is very widespread in nature, found in the free state and in various compounds; in the free state it is found in the air, in water; in the form of compounds (MgCO₃, FeCO₃, limestone) it is part of the earth's crust. The presence of CO₂ in water gives it the ability to dissolve various salts (phosphoric, calcium carbonate), as a result of which the destruction of rocks occurs. Carbon dioxide is released by volcanoes, from mountain cracks, in some caves, springs, etc. Carbon dioxide is formed during respiration of animals and plants, during decay and fermentation, during combustion of organic substances. The green parts of plants in the light absorb CO₂ and form carbohydrates from it (see Assimilation, Carbohydrates). In the animal body carbon dioxide is present as a product of oxidation of organic substances, in tissues and fluids - both in the free state and in combination, in the form of carbonates. Carbon dioxide is a respiratory hormone that acts as an irritant to the respiratory center (see Respiration, Blood Gases). The release of carbon dioxide from the blood in the lungs requires its preliminary transformation of H₂CO₃ into anhydride, CO₂. Meldrum and Roughton believe that this process (as well as the hydration of CO₂ into H₂CO₃) is catalyzed by a special enzyme (carbonic anhydrase). Carbonic acid and its salts are one of the main buffers of the blood, maintaining the constancy of its active reaction (see). The amount of carbon dioxide released is judged by the intensity of metabolic processes in the body. To determine the carbon dioxide released during respiration, methods of Pettenkofer, Peterson-Palmquist, and others are used. Pettenkofer's method is based on the absorption of carbon dioxide by a solution of barium hydroxide and determining the excess of the latter by titration. A simpler and faster method is that of Peterson-Palmquist. Carbon dioxide and its compounds have wide practical application. Carbonated waters are used for medicinal purposes in the form of baths and internally. It is believed that carbon dioxide acts as a stimulant on gastric secretion. Carbonated water quenches thirst well, which is why it is recommended to drink it during work at high temperatures. Carbon dioxide is used in chemical productions in the preparation of soda, white lead, etc. Carbon dioxide is obtained in factories either by burning coal or by the action of acids on lime; it can also be obtained by calcining dolomite (MgCO₃) and other compounds. In laboratories, to obtain carbon dioxide, Kipp's apparatus is used, acting on marble with hydrochloric acid.